"Eric Greenwell" wrote in message
...
Dave Rolley wrote:
In the USA there are simple and fatal flaws with any system that
includes ground based radar and a controller near a high density
airport.

First, as already mentioned, the controller's normal display is
processed information. The is often referred to as secondary radar.
Basically it is just the transponder equipped traffic with data tags.

Second, as already mentioned, the system is normally configured to drop
out targets that have a low ground speed or don't have a ground track
that is going somewhere (e.g. circling). So a radar reflector wouldn't
be much help. It isn't the size of the return that gets the target
filtered out under these circumstances.

Third, and probably the greatest problem, if there are too many 12XX
returns (VFR transponder equipped traffic in the USA) the controller can
filter the specific codes or blocks of codes.

These may be "simple" flaws, but they aren't "fatal" to transponder
equipped gliders:

#1 this isn't a problem for transponder equipped aircraft, since they
will show on the display along with their data tag. Primary returns may

not be displayed, depending on the situation; however, if you call ATC,
they may be able and willing to put your primary return on the screen.

#2 doesn't apply to transponder equipped aircraft, as they are not
filtered by speed or track, but may apply to aircraft without
transponders, as primary returns may be filtered by speed or track.
Filtering out transponder

#3 applies in only a very few, very high density areas that gliders
aren't likely to be flying in, such as the area near LAX (Los Angles).

The was a mid-air between a commuter flight and a skydiving jump plane
between Denver CO and Cheyenne WY about 15 or 20 years ago. The
commuter flew into the climbing jump plane. Since they we both above
12,500 MSL (about 7,000 AGL), it was assumed the commuter pilots were
heads down in the cockpit. The jump plane was using a transponder code
of 1234 and ATC had 12XX code filtered for the higher altitudes. The
jump plane was not talking to ATC. Oops...

Errors happen, and this has got to be a rare one, where both ATC and the
jump plane make them. I've asked the controllers at Seattle Center if
they ever filter out VFR code 1200 - "NO SIR"! The jump plane flying out
of our airport gets every transponder equipped aircraft (including my
glider) called out to him before he lets any jumpers loose.

Other than a TCAS installation (aircraft to aircraft),

This is actually the BEST reason to carry a transponder - so airliners
in particular, but also many corporate aircraft and military aircraft
can avoid you!

the only way a
transponder will help us is if the ATC facility in the area knows about
the glider operations and can (or will) operate their equipment in a
manner that allows the controller to see the glider traffic. That means
we have to work with the local ATC folks. Otherwise, it is so much extra
ballast and power draw in the glider.

THis is definitely NOT true. ATC is operating their equipment so they
can track VFR aircraft (that includes you in your glider), and they
don't need to know if it's an airplane or a glider. If they can see the
airplanes, they'll see you, even if you are circling or moving slowly.


Even when the technology should help, local procedures can negate the
technology. Since the way we operate gliders does not fit in the
general transportation model the ATC system is designed to support,
putting a transponder into a glider without working with the affected
ATC organization does little to help the situation.

The essence of the VFR 1200 code is that ATC _doesn't_ need to "work"
with you: that's why it's a "VFR" code. You just fly around, minding
your own business like the airplanes flying VFR, and their radar will
pick you up. They want to know where the VFR traffic is so they can
direct the IFR traffic away from it. Folks, we aren't that special. The
only place in the USA that I know of that has a different situation is
at Reno, where gliders may use the 0440 code to identify themselves as a
glider. It's not required that gliders use it, only that they are
allowed to use it as an aid to the Reno controllers. If you use 1200,
they'll still see you.

Note that it's not just the IFR and TCAS traffic that can be steered
away from you, but also VFR aircraft using "flight following", and the
already mentioned skydivers.

If you think you need a transponder, but are concerned that it will be
just "so much extra ballast and power draw", please, please, contact the
ATC in your flying area and ask them if they will see you on their
radar! My experience is they will be delighted to have you equipped with
one.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Eric, I think you got all that right.

I have spoken to the Denver Center about transponders in gliders.
Specifically, I asked if "Flight Following" would be available to
transponder equipped gliders after explaining the erratic path gliders fly.
The answer was, "On a workload permitting basis, of course". (They also
mentioned that the "erratic" description would fit some of the instrument
training flights they work.)

"Flight following" means that you get your very own transponder code for
that flight and somebody to talk to if you're in trouble. Workload
permitting, they will call out your position to other conflicting traffic
and tell you about them. You're guaranteed to be on their radar screens
until the end of the flight or until you get a call from center that "Flight
following is terminated" due to workload.

The downside is that you would have to constantly monitor the center
frequency listening to all the other chatter. You can leave the frequency
for short periods by request to contact your crew.

For those readers outside the USA, this is as close as we get to "Controlled
VFR". For those properly trained and equipped, Flight Following morphs
nicely into an IFR clearance if the need arises.

I always used flight following in place of a flight plan when flying powered
aircraft. I made sure whoever I was meeting at my destination knew my ETA,
my N number and who to call. I didn't have to remember to cancel it and, if
I went down, the radar track would pinpoint my location.

Bill Daniels